The ultimate purpose of the present study was to investigate the effectiveness of portfolio on developing English vocabulary for non-English Majors at Al-Arich Faculty of Education. The subjects of the present study were 79 first year colleges who were randomly selected and assigned into two groups of the study. The tools used in this study were The Pre-Post Students' Vocabulary Test "The Pre-Post SVT", The Post Experiment Students' Questionnaire "PESQ", A Checklist for Portfolio Self, Peer and Rater Assessment, and The portfolio Program. The portfolio program was administered to the experimental group in the first term of the academic year 2006-2007 at Al-Arich Faculty of Education. Results showed that the portfolio program was effective in developing the experimental group vocabulary and self assessment skills. Analyzing student' portfolio entries showed improvement of students performance .Moreover, the results of the PESQ showed a great deal of satisfaction among students regarding the use of portfolios. Generally, Students felt that the portfolio program was useful and valid. Recommendations and suggestions for further studies were provided.